Transformer



Dec. 18, 1951 DOLE 2,579,308

TRANSFORMER Filed Nov. 4. 1948 Inv'efitorw' Mar-"s hall H. Dole,

His Attorney.

Patented Dec. 18, 1951 TRANSFORMER Marshall H. Dole, Hudson, Ind.,asslgnor to General Electric Company, a corporation of New YorkApplication November 4, 1948, Serial No. 58,297

3 Claims. 1

This invention relates to an electric induction apparatus and moreparticularly to the construction of a magnetic core for an electrictransformer device.

By utilizing a new and novel magnetic core construction which employscontiguous wedgeshaped segments of magnetic material bound together soas to form a cylindrical core numerous advantages result. In order tobetter explain what these advantages are and why they are the naturalconsequence of the invention disclosed in this application it will beadvantageous. to explain, in concise terms, the nature of the invention.A cylindrical central winding leg of a magnetic core for stationaryinduction apparatus is constructed from a plurality of wedge-shapedsegments which are maintained in intimate contact to one another.Mounted on this winding leg are the coils associated with the inductiondevice. A magnetic yoke which surrounds the coils and serves tomagnetically link the coils together is also constructed of wedge-shapedsegments and is contiguous, in part with the central winding leg. Thusthe yoke may be visualized as a hollow cylinder which accommodateswithin it the central winding leg and its associated windings.

The advantages this construction offers are manifold. Noise due to theleakage of flux into nearby magnetic materials is reduced since flux'leakage is reduced to a minimum by having the coils completelysurrounded by the yoke member. A substantial saving results in thewinding of coils which are mounted on a cylindrical core. This is due tothe fact that the coils may be circular thus eliminating sharp corners.Since there are no sharp corners there is very little danger offracturing insulation which may be incorporated on the surface of thewire. Thus the necessity of insulating each layer of wire by the use ofan insulating material, such as paper, in addition to the insulation onthe wire itself, is eliminated. Also since the winding leg is round andthe coils are round less copper need be used in the circular coils thanin the conventional type of coils where there are spaces between thecoil and the winding leg due to the necessity of winding the copperaround sharp corners. Since the yoke member surrounds the centralwinding leg and no coils areexposed, additional encasing means is notnecessary and all that need be provided are caps which enclose each endof the core and provide means for mounting the induction apparatus.Insulating compound, which is very often used to fill the space betweenthe enclosed electric device and its encasin means is eliminated.Another advantage of the construction disclosed by this inventionresults from the fact that air gaps separating the winding leg from theyoke member have much greater width, since they cover 360 degrees, thanin a similar device using conventional fiat laminations. Also animportant consequence of this invention is that noise due to thevibration of the wedges making up the core, this vibration resultingfrom the magnetic stresses set up between these wedges as aconsequenceof the cyclic variation of current in the coils, is reduced.This is accomplished by the core clamping operation which forces all thewedges of the core more tightly together reducing audible vibrations.

It is an object of this invention to provide a core construction forelectric induction apparatus which substantially eliminates the presenceof noise in such devices.

Another object of this invention is to provide a core construction forelectric induction apparatus which allows a minimum of leakage flux.

Still another object of this invention is to provide an electricinduction apparatus which needs no additional encasing means, and theuse of insulating compound is eliminated.

A further object of this invention is to allow the use of round coilsallowing a saving in the total amount of copper to be used.-

Another object of this invention is to provide a core for electricinduction apparatus which is constructed of wedge-shaped segments ofmagnetic material.

This invention has particular application to the construction of afluorescent lamp ballast, though it is in no way limited thereto, and inthe following description taken in connection with the accompanyingdrawing it will be described as applied to the construction of such adevice.

In the drawing, the single figure shown is a perspective view of atwo-lamp fluorescent ballast constructed in accordance with thisinvention.

Referring now to the drawing there is shown therein a two-lampfluorescent ballast I having a central winding leg 2 which isconstructed of wedge-shaped segments of magnetic material. Thewedge-shaped segments are forced into intimate contact with one anotherso as to form the hollow cylindrical central winding leg 2. Mounted onthe winding leg 2, in the illustrated case, is a primary coil 3 and thetwo secondary windings 4 and 5. To complete the magnetic path so as toallow for the coupling of the primary and secondary coils 3, 4 and 5 amagnetic yoke 8 is constructed of wedge-shaped segments I, mounted incontiguity, so as to completely surround the transtormer coils 3, 4 and5.

Since the fluorescent ballast l is used in a circuit with an electricdischarge device, which possesses negative resistance characteristics,it must provide means for limiting the flow of circuit current onceconduction through the fluorescent lamp has been initiated. Circuitreactance is provided by having a high internal leakage reactance whichis achieved by employing the shunts 8 and 9 located between the primarycoil 3 and the secondary coil 4 and the primary coil 3 and the secondarycoil 5, respectively. The shunts 8 and 9 are formed as integral parts ofthe yoke segments 1. In order to prevent the leakage fiux paths fromhaving too low a reluctance it is usually necessary to provide them witha high reluctance section, such as an air gap, and it has also beenfound that desirable results are obtained when a portion of the core isprovided with a bridged gap. In the figure, the air gap i separates theshunt leg 8 from the central winding leg 2, and the air gap II separatesthe,

shunt leg 9 from the central winding leg 2. A bridged gap 12 is providedat one end of the core as shown in the illustration. It can be seen thatin cross-section the ballast construction provided by this inventionappears to be' very similar to that shown in the patent applicationSerial No. 776,082, filed September 25, 1947 in the name of Wesley W.Brooks, and assigned to the same assignee as the present invention.

Since the transformer coils 3, 4, and 5 are entirely surrounded by themagnetic yoke 6 means must be provided for allowing the electrical leadsfrom the coils to be connected to their co-operating circuit. ,This isaccomplished by employing one magnetic wedge 13 in the yoke 6 which ishollowed out so as to provide room to accommodate the lead wires l4.Encasing means completely enclosing the core is not necessary and allthat need be provided are end caps I5 and I6 which clamp the wedges 6together as a unit. The end caps l5 and I6 may have mounting feet I!associated with them so as to provide means for securing the fluorescentlamp ballast i to its associated equipment.

The transformer may be assembled as follows: First, a suflicient numberof the wedge-shaped laminations or segments for forming the winding leg2 are placed against each other until the cylindrical winding leg 2 isformed. Then the windings 3, 4 and 5 are pressed on to the Winding legassembly so as to hold it together and the coils or windings areproperly spaced so as to receive the magnetic shunt members 8 and 9.Then leads are attached to the coils or else previously attached leadsfor the coils are aligned by turning the coils the proper amount andthen these leads are encased in the hollow wedge-shaped segment [3.Additional wedge-shaped segments 1 are then successively placed againsteach other and against the segment l3 until the cylindrical yoke memberis built up with the magnetic shunt portions 8 between the coils 3 and 4and the magnetic shunt portions 9 between the coils 3 and 5. Then theclamping caps 5 and 6 are pressed on the ends of the completed assemblyso as to hold the unit to ether.

While there has been shown and described a particular embodiment of thisinvention it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A magnetic core for stationary induction apparatus comprising, asubstantially cylindrical central winding leg member, said winding legmember constructed of a plurality of wedgeshaped winding leg sections,said wedge-shaped winding leg sections maintained in contiguousrelationship to one another, a yoke member similarly constructed of aplurality of contiguous wedge-shaped yoke sections, each of saidwedgeshaped yoke sections having a plurality of sidewise extending legsincluding end legs and at least one intermediate leg, said yoke membershaving a substantially hollow cylindrical shape, the opening thereinhaving a minimum diameter approximately equal to the outer diameter ofsaid central winding leg member, portions'of said end legs of saidwedge-shaped yoke sections being contiguous with said winding legmember, said yoke member substantially surrounding said winding legmember, and clamping means surrounding the ends of said yoke member forholding said sections in assembled relation.

2. A magnetic core for stationary induction apparatus comprising, asubstantially cylindrical central winding leg member, said winding legmember constructed of a plurality of wedgeshaped winding leg sections,said wedge-shaped winding leg sections maintained in contiguousrelationship to'one another, a yoke member similarly constructed of aplurality of contiguous wedge-shaped yoke sections, each of saidwedgeshaped yoke sections having a plurality of sidewise extending legsincluding end legs and intermediate legs, said end legs being longerthan said intermediate legs, said yoke member having a substantiallyhollow cylindrical shape, the opening therein having a minimum diameterapproximately equal to the outer diameter of said central winding legmember, portions of said end legs of said wedge-shaped yoke sectionsbeing contiguous with said winding leg member, air gaps separating saidintermediate legs of said wedge-shaped yoke sections from said windingleg member, one of said end legs forming a bridged-gap joining saidwinding leg member and said yoke member, said yoke member substantiallysurrounding said winding leg member, and cup-shaped clamping meanssurrounding the ends of said yoke member for holding said sections inassembled relation.

3. A two-lamp fluorescent ballast comprising, a substantiallycylindrical central winding leg member, said winding 18g memberconstructed of a plurality of wedge-shaped winding leg sections, each ofsaid wedge-shaped winding leg sections formed as a portion of a hollowcylinder, said wedge-shaped winding leg sections maintained incontiguous relationship to one another, said central winding leg memberhaving a plurality of induction coils mounted thereon, a yoke membersimilarly constructed of a plurality of contiguous wedge-shaped yokesections, each of said wed e-shaped yoke sections having a plurality ofsidewise extending legs including end legs and intermediate legs, saidend legs being longer than said intermediate legs, said yoke memberhaving a substantially hollow cylminimum diameter approximately equal tothe outer diameter of said central winding leg member, said end legs ofsaid wedge-shaped yoke sections bein contiguous with said winding legmember, said induction coils occupying the spaces between said legs 01said wedge-shaped yoke sections, air gaps separating said intermediatelegs of said wedge-shaped yoke sections from said winding leg member,one of said end legs forming a bridged-gap joining said winding legmember and said yoke member, said yoke member substantially surroundinsaid winding leg member, at least one of said wedge-shaped yoke sectionshaving ahollow portion, the conductive leads fastened to said inductioncoils being housed within said hollow portion of said last mentionedwedge-shaped yoke section, and cup-shaped clamps encompassing the endsof 6 said fluorescent lamp ballast so as to hold the The followingreferences are of record in the tile 01 this patent:

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